Metabolite diffusion provide the unique ability to study the intracellular environment of specifi... more Metabolite diffusion provide the unique ability to study the intracellular environment of specific cell types of the brain. Multiple studies suggest that the diffusivity along dendrites and axons is time dependent due to variations in diameter. We explore the signal due to such effects in Monte Carlo simulations in settings feasible for preclinical PGSE measurements and find that time dependent kurtosis, but not diffusivity provide the most potent source of contrast to this effect. We observe similar effects of intraneuronal NAA diffusion in rat.
In-vivo Manganese-Enhanced MRI (MEMRI) studies have shown important potential in rodents for the ... more In-vivo Manganese-Enhanced MRI (MEMRI) studies have shown important potential in rodents for the delineation of cytoarchitectural brain features and of functional details. Ex-vivo MEMRI on the other hand offers the possibility to investigate brain microstructure and function with improved spatial resolution and no motion artefacts. Here, ex-vivo lamb brains were immersed in a highly concentrated MnCl2 solution for a month and revealed interesting cytoarchitectural features already 24 hours after immersion and up to 3 months after the end of immersion on MPRAGE images at 3T. A novel ex-vivo MEMRI approach is proposed, which could benefit MEMRI translation to human studies.
ABSTRACTThe hypothalamus is a central structure of the mammalian brain, which controls physiologi... more ABSTRACTThe hypothalamus is a central structure of the mammalian brain, which controls physiological, endocrine and metabolic brain homeostasis. Despite this essential role, little is known about the normal and altered neurochemical changes occurring within the hypothalamic structures. Here, the metabolism of the hypothalamus of ewes was investigated at 3T using proton magnetic resonance spectroscopy (1H-MRS). We used the sensitivity of these animals to photoperiod i.e. the ratio of day to night length, to investigate the hypothalamic metabolic changes and their relationship to hypothalamic adult neurogenesis. A longitudinal study involving 4 ewes per timepoint was conducted at 4 time points (P01, P02, P03 and P04) during long days (LD) and 4 time points during short days (SD). Significant metabolic changes were found between LD and SD at all time points in particular for glutamate (Glu), glutamine, myo-inositol and total N-acetyl-Aspartate (NAA). During SD, glutamate and glutamine ...
Adult neurogenesis (AN) can be defined as the birth and development of new neurons in adulthood. ... more Adult neurogenesis (AN) can be defined as the birth and development of new neurons in adulthood. Until the 1990s, AN was deemed not to happen after birth. Gradually, several groups demonstrated that specific zones of the brain of various species had a neurogenic potential. AN could be the key to treating a large range of neurodegenerative, neuropsychiatric, and metabolic diseases, with a better understanding of the mechanisms allowing for regeneration of new neurons. Despite this promising prospect, the existence of AN has not been validated in vivo in humans and therefore remains controversial. Moreover, the weight of AN-induced plasticity against other mechanisms of brain plasticity is not known, adding to the controversy. In this review, we would like to show that recent technical advances in brain MR imaging methods combined with improved models can resolve the debate.
Substantial research on the association between early-life stress and its long-lasting impact on ... more Substantial research on the association between early-life stress and its long-lasting impact on lifetime mental health has been performed revealing that early-life environmental adversity strongly regulates brain function. Alterations of gene expression and behavior in the off-springs of paternally stressed rats were also revealed. However, the precise mechanisms underlying these changes remain poorly understood. Here, an improved characterization of these processes from investigations of the functional metabolism of animal models exposed to peripubertal stress (PS) is proposed. The ultimate goal of this study was to bring forward functional Magnetic Resonance Spectroscopy (fMRS) as a technique of interest for a better understanding of brain areas by endogenous stimulators such as stress. The present study evaluated, compared and classified effects of individual PS (iPS) and paternal PS (pPS) under corticosterone (CORT) challenge in the septal areas of adult rats. Acute stress was ...
PurposeThis study aimed to characterize Blood oxygen level-dependent (BOLD) effects in1H-MR spect... more PurposeThis study aimed to characterize Blood oxygen level-dependent (BOLD) effects in1H-MR spectra obtained during optogenetic activation of the rat forelimb cortex for the correction and estimation of accurate metabolite concentration changes.MethodsT2*-induced effects were characterized by linewidth changes and amplitude changes of water, NAA and tCr spectral peaks during the stimulation paradigm. Spectral linewidth-matching procedures were used to correct for the line-narrowing effect induced by BOLD. For an increased understanding of spectroscopic BOLD effects and the optimized way to correct them, a 1 Hz line-narrowing effect was also simulated on mouseproton MR spectrum1H-fMRS data acquired using STEAM acquisitions at 9.4T in rats (n=8) upon optogenetic stimulation of the primary somatosensory cortex were used. Data were analyzed with MATLAB routines and LCModel. Uncorrected and corrected1H-MR spectra of simulated and in-vivo data were quantified and compared. BOLD-corrected ...
The ovine model could be an effective translational model but remains underexplored. Here, Blood ... more The ovine model could be an effective translational model but remains underexplored. Here, Blood Oxygen Level dependent functional MRI during visual stimulation and resting-state perfusion MRI were explored. We aimed at investigating the impact of isoflurane anesthesia during visual stimulation and evaluate resting cerebral blood flow and cerebral blood volume parameters in the lamb and adult sheep brain. BOLD fMRI and perfusion MRI after a bolus of DOTAREM were conducted in 4 lambs and 6 adult ewes at 3T. A visual stimulation paradigm was delivered during fMRI at increasing isoflurane doses (1- 3%). Robust but weak BOLD responses (0.21± 0.08%) were found in the lateral geniculate nucleus (LGN) up to 3% isoflurane anaesthesia. No significant differences were found beween BOLD responses in the range 1 to 3 % ISO (p>0.05). However, LGN cluster size decreased and functional localization became less reliable at high ISO doses (2.5-3% ISO). BOLD responses were weaker in adult sheep than in lambs (4.6 ± 1.5 versus 13.6 ± 8.5; p=0.08). Relative cerebral blood volumes (rCBV) and relative cerebral blood flows (rCBF) were significantly higher (p< 0.0001) in lambs than in adult sheep for both gray and white matter. The impact of volatile anesthesia was explored for the first time on BOLD responses demonstrating increased reliability of functional localization of brain activity at low doses. Perfusion MRI was conducted for the first time in both lambs and adult ewes. Assessment of baseline cerebrovascular values are of interest for future studies of brain diseases allowing an improved interpretation of BOLD responses.
Biomedical investigations in clinically relevant animal models is of crucial interest for faster ... more Biomedical investigations in clinically relevant animal models is of crucial interest for faster and appropriate transfer to human. The ovine model has already demonstrated its potential compared to rodents and non-human primates (NHP) in various studies: sheep possess a gyrencephalic brain, captivity is not an issue and can undergo magnetic resonance imaging (MRI) in routine clinical scanners (1.5T, 3T) under identical conditions using similar techniques to humans. To date, the effects of anesthesia have been poorly explored and only few functional MRI (fMRI) studies were conducted in sheep. Here, Blood Oxygen Level dependent fMRI and perfusion MRI were conducted in lambs and adult ewes at 3 T. Robust but weak BOLD responses to visual stimulation were found in the lateral geniculate nucleus (LGN) up to 3% isoflurane anaesthesia. BOLD responses were weaker in adult sheep than in lambs while relative cerebral blood volumes (rCBV) and relative cerebral blood flows (rCBF) were signific...
Knowledge about biochemical processes is a prerequisite for a better understanding of mechanisms ... more Knowledge about biochemical processes is a prerequisite for a better understanding of mechanisms underlying brain activity. 1 H functional magnetic resonance spectroscopy (1 H-fMRS) at high magnetic fields allows for the non-invasive measurement of metabolic changes during brain activation. Optogenetics, on the other hand, has revolutionized the field of neuroscience. It was previously coupled with functional magnetic resonance imaging (fMRI) techniques in rodents enabling population-specific targeting of cells, investigating brain networks with unprecedented in vivo precision.
Introduction: Sleep-fragmentation (SF) is a common symptom associated to disturbances such as sle... more Introduction: Sleep-fragmentation (SF) is a common symptom associated to disturbances such as sleep apneas (1) Previous studies showed that SF induces daytime sleepiness and cognitive impairments associated to metabolic changes (2, 3). In the present study, the neurochemical profile of mice submitted to SF during 14 days was examined using H-MRS at 14.1T both in hippocampus and the frontal cortex. The goal of this study was to investigate changes linking sleep fragmentation to modifications in neurotransmitter concentrations. Materials and Methods: Animal preparation: C57BL6 mice (n=10, BW=25±2g) were individually transferred in rotating Plexiglas cylindrical cages equipped with three internal Plexiglas static walls to be submitted to SF. The rotations consisted in a mild rotation (1.5 rpm) of the floor of the cages lasting 20s every minute. Such a rotation brings the mouse in contact with one of the walls and wakes it up. Animals had free access to food and water. Each mouse was left to adapt to its new environment for a week before the first MRS session and prior to the start of the cage rotation to prevent stress. Mice underwent a first MRS session in their basal state and a second MRS 14days after .Prior to MRS, mice were gently manipulated to avoid stress and anesthetized with 2% isoflurane in a mixture of O2 and N2O. Each of them was positioned in a dedicated mouse holder equipped with ear and teeth bars and anesthetized with 1% isoflurane in O2/N2O through a nose cone. Body temperature was maintained at 36.5±1oC by circulating warm water around the animals.H-MRS All the experiments were performed on a 14.1T/26cm horizontal bore magnet ( Magnex, Varian). A quadrature T/R 14-mm surface coil was used. Localized proton spectroscopy was performed using SPECIAL (4) in a 4±1μl voxel for the hippocampus and in a 12±1μl voxel for the frontal cortex placed using multi-slice fast spin echo (FSEMS) images. Field homogeneities were adjusted using FASTMAP (5) up to water linewidth=20-25Hz. At least 40 blocks of 16 FIDs were acquired for a total acquisition time of 40minutes. Metabolite concentrations were calculated using LCmodel (6). A paired t-test was used to compare pre and post-SF metabolite concentrations. A pvalue<0.05 was considered significant. Results: Fig.1a and 1b present the comparison of mean metabolite concentrations pre and post-SF in the hippocampus and the frontal cortex respectively. In the hippocampus, mean GABA concentrations decreased significantly between basal and SF states (pvalue =0.006) and a significant decrease was also detected for lactate (pvalue<0.05). In the cortex, no significant differences were observed between basal and SF states, however a tendency to decrease was also observed for GABA (pvalue=0.21). In Fig.2, the evolution of GABA, and Lactate concentrations between basal and SF states are shown individually in the hippocampus (Black) and in the cortex (red).
Target Audience: Physicist, Neuroscientists, Biochemists Introduction: Recently, the importance o... more Target Audience: Physicist, Neuroscientists, Biochemists Introduction: Recently, the importance of thalamocortical projections (TC) to the primary somatosensory cortex (S1) has generated a lot of interest 1 .Thalamic nuclei such as the VPM and POM represent an important relay for functional information processing of the ascending response to whisker or forepaw stimulations. Moreover, TC inputs to S1 are known to modulate both glutamatergic and GABAergic transmissions 2. However, the metabolic mechanisms of regulation of the barrel cortex by TC transmissions remain unclear. Changes of metabolite concentrations in S1 of rats during stimulation have been evaluated using functional proton magnetic resonance spectroscopy (fMRS) 3,4. In the present study, fMRS was conducted in the primary somatosensory barrel field cortex and in the thalamus during rest and functional stimulation. In addition, the underlying mechanisms of glutamatergic and GABAergic transmissions from thalamus to barrel c...
An improved activity-induced manganese-dependent MRI study of the rat barrel cortex Purpose: In 1... more An improved activity-induced manganese-dependent MRI study of the rat barrel cortex Purpose: In 1997, Lin et al. (1) proposed an alternative to BOLD functional MRI to image brain function using Manganese. The paramagnetic properties of Mn2+ ions allowed for the first time the indirect measurement of neuronal activation through activity-induced manganese-dependent (AIM) MRI. However, the technique highly depends on the permeability of Mn2+ ions through the blood brain barrier and the minimization of their toxicity. Aoki et al. (2,3) further described the potential of AIM MRI and ways to overcome these difficulties. Nonetheless, although the technique is very attractive and promising for direct monitoring of regional brain activation independent of hemodynamic changes, it remains difficult and has not yet been extensively used. Here, we propose an optimized AIM MRI investigation of the rat somatosensory cortex under tight physiological follow up and an histogram analysis for an increa...
ABSTRACTThe electronic and nuclear stopping effects produced by MeV ion bombardment in polyethyle... more ABSTRACTThe electronic and nuclear stopping effects produced by MeV ion bombardment in polyethylene (PE) and polyvinylidene chloride (PVDC) have been previously studied and reported. We have subsequently selected two other insulators: polystyrene (PS) and polyethersulfone (PES) which contains sulfur as a crosslinking agent, and irradiated them with MeV alpha particles. The electronic and nuclear effects of the incident ions were separated by stacking thin films of the polymers. A layered system was selected such that the first layers experienced most of the effects of the electronic energy deposited and the last layers received most of the effects of the nuclear stopping. The changes in the chemical structure were measured by residual gas analysis (RGA), Raman microprobe analysis, RBS and FTIR. The post-irradiation characterization resolved the effects of the stopping powers on the PS and PES and the results were compared with those from PE and PVDC.
By definition, tumours are heterogeneous. They are defined by marked differences in cells, microe... more By definition, tumours are heterogeneous. They are defined by marked differences in cells, microenvironmental factors (oxygenation levels, pH, VEGF, VPF and TGF-α) metabolism, vasculature, structure and function that in turn translate into heterogeneous drug delivery and therapeutic outcome. Ways to estimate quantitatively tumour heterogeneity can improve drug discovery, treatment planning and therapeutic responses. It is therefore of paramount importance to have reliable and reproducible biomarkers of cancerous lesions' heterogeneity. During the past decade, the number of studies using histogram approaches increased drastically with various magnetic resonance imaging (MRI) techniques (DCE-MRI, DWI, SWI etc.) although information on tumour heterogeneity remains poorly exploited. This fact can be attributed to a poor knowledge of the available metrics and of their specific meaning as well as to the lack of literature references to standardised histogram methods with which surroga...
Metabolite diffusion provide the unique ability to study the intracellular environment of specifi... more Metabolite diffusion provide the unique ability to study the intracellular environment of specific cell types of the brain. Multiple studies suggest that the diffusivity along dendrites and axons is time dependent due to variations in diameter. We explore the signal due to such effects in Monte Carlo simulations in settings feasible for preclinical PGSE measurements and find that time dependent kurtosis, but not diffusivity provide the most potent source of contrast to this effect. We observe similar effects of intraneuronal NAA diffusion in rat.
In-vivo Manganese-Enhanced MRI (MEMRI) studies have shown important potential in rodents for the ... more In-vivo Manganese-Enhanced MRI (MEMRI) studies have shown important potential in rodents for the delineation of cytoarchitectural brain features and of functional details. Ex-vivo MEMRI on the other hand offers the possibility to investigate brain microstructure and function with improved spatial resolution and no motion artefacts. Here, ex-vivo lamb brains were immersed in a highly concentrated MnCl2 solution for a month and revealed interesting cytoarchitectural features already 24 hours after immersion and up to 3 months after the end of immersion on MPRAGE images at 3T. A novel ex-vivo MEMRI approach is proposed, which could benefit MEMRI translation to human studies.
ABSTRACTThe hypothalamus is a central structure of the mammalian brain, which controls physiologi... more ABSTRACTThe hypothalamus is a central structure of the mammalian brain, which controls physiological, endocrine and metabolic brain homeostasis. Despite this essential role, little is known about the normal and altered neurochemical changes occurring within the hypothalamic structures. Here, the metabolism of the hypothalamus of ewes was investigated at 3T using proton magnetic resonance spectroscopy (1H-MRS). We used the sensitivity of these animals to photoperiod i.e. the ratio of day to night length, to investigate the hypothalamic metabolic changes and their relationship to hypothalamic adult neurogenesis. A longitudinal study involving 4 ewes per timepoint was conducted at 4 time points (P01, P02, P03 and P04) during long days (LD) and 4 time points during short days (SD). Significant metabolic changes were found between LD and SD at all time points in particular for glutamate (Glu), glutamine, myo-inositol and total N-acetyl-Aspartate (NAA). During SD, glutamate and glutamine ...
Adult neurogenesis (AN) can be defined as the birth and development of new neurons in adulthood. ... more Adult neurogenesis (AN) can be defined as the birth and development of new neurons in adulthood. Until the 1990s, AN was deemed not to happen after birth. Gradually, several groups demonstrated that specific zones of the brain of various species had a neurogenic potential. AN could be the key to treating a large range of neurodegenerative, neuropsychiatric, and metabolic diseases, with a better understanding of the mechanisms allowing for regeneration of new neurons. Despite this promising prospect, the existence of AN has not been validated in vivo in humans and therefore remains controversial. Moreover, the weight of AN-induced plasticity against other mechanisms of brain plasticity is not known, adding to the controversy. In this review, we would like to show that recent technical advances in brain MR imaging methods combined with improved models can resolve the debate.
Substantial research on the association between early-life stress and its long-lasting impact on ... more Substantial research on the association between early-life stress and its long-lasting impact on lifetime mental health has been performed revealing that early-life environmental adversity strongly regulates brain function. Alterations of gene expression and behavior in the off-springs of paternally stressed rats were also revealed. However, the precise mechanisms underlying these changes remain poorly understood. Here, an improved characterization of these processes from investigations of the functional metabolism of animal models exposed to peripubertal stress (PS) is proposed. The ultimate goal of this study was to bring forward functional Magnetic Resonance Spectroscopy (fMRS) as a technique of interest for a better understanding of brain areas by endogenous stimulators such as stress. The present study evaluated, compared and classified effects of individual PS (iPS) and paternal PS (pPS) under corticosterone (CORT) challenge in the septal areas of adult rats. Acute stress was ...
PurposeThis study aimed to characterize Blood oxygen level-dependent (BOLD) effects in1H-MR spect... more PurposeThis study aimed to characterize Blood oxygen level-dependent (BOLD) effects in1H-MR spectra obtained during optogenetic activation of the rat forelimb cortex for the correction and estimation of accurate metabolite concentration changes.MethodsT2*-induced effects were characterized by linewidth changes and amplitude changes of water, NAA and tCr spectral peaks during the stimulation paradigm. Spectral linewidth-matching procedures were used to correct for the line-narrowing effect induced by BOLD. For an increased understanding of spectroscopic BOLD effects and the optimized way to correct them, a 1 Hz line-narrowing effect was also simulated on mouseproton MR spectrum1H-fMRS data acquired using STEAM acquisitions at 9.4T in rats (n=8) upon optogenetic stimulation of the primary somatosensory cortex were used. Data were analyzed with MATLAB routines and LCModel. Uncorrected and corrected1H-MR spectra of simulated and in-vivo data were quantified and compared. BOLD-corrected ...
The ovine model could be an effective translational model but remains underexplored. Here, Blood ... more The ovine model could be an effective translational model but remains underexplored. Here, Blood Oxygen Level dependent functional MRI during visual stimulation and resting-state perfusion MRI were explored. We aimed at investigating the impact of isoflurane anesthesia during visual stimulation and evaluate resting cerebral blood flow and cerebral blood volume parameters in the lamb and adult sheep brain. BOLD fMRI and perfusion MRI after a bolus of DOTAREM were conducted in 4 lambs and 6 adult ewes at 3T. A visual stimulation paradigm was delivered during fMRI at increasing isoflurane doses (1- 3%). Robust but weak BOLD responses (0.21± 0.08%) were found in the lateral geniculate nucleus (LGN) up to 3% isoflurane anaesthesia. No significant differences were found beween BOLD responses in the range 1 to 3 % ISO (p>0.05). However, LGN cluster size decreased and functional localization became less reliable at high ISO doses (2.5-3% ISO). BOLD responses were weaker in adult sheep than in lambs (4.6 ± 1.5 versus 13.6 ± 8.5; p=0.08). Relative cerebral blood volumes (rCBV) and relative cerebral blood flows (rCBF) were significantly higher (p< 0.0001) in lambs than in adult sheep for both gray and white matter. The impact of volatile anesthesia was explored for the first time on BOLD responses demonstrating increased reliability of functional localization of brain activity at low doses. Perfusion MRI was conducted for the first time in both lambs and adult ewes. Assessment of baseline cerebrovascular values are of interest for future studies of brain diseases allowing an improved interpretation of BOLD responses.
Biomedical investigations in clinically relevant animal models is of crucial interest for faster ... more Biomedical investigations in clinically relevant animal models is of crucial interest for faster and appropriate transfer to human. The ovine model has already demonstrated its potential compared to rodents and non-human primates (NHP) in various studies: sheep possess a gyrencephalic brain, captivity is not an issue and can undergo magnetic resonance imaging (MRI) in routine clinical scanners (1.5T, 3T) under identical conditions using similar techniques to humans. To date, the effects of anesthesia have been poorly explored and only few functional MRI (fMRI) studies were conducted in sheep. Here, Blood Oxygen Level dependent fMRI and perfusion MRI were conducted in lambs and adult ewes at 3 T. Robust but weak BOLD responses to visual stimulation were found in the lateral geniculate nucleus (LGN) up to 3% isoflurane anaesthesia. BOLD responses were weaker in adult sheep than in lambs while relative cerebral blood volumes (rCBV) and relative cerebral blood flows (rCBF) were signific...
Knowledge about biochemical processes is a prerequisite for a better understanding of mechanisms ... more Knowledge about biochemical processes is a prerequisite for a better understanding of mechanisms underlying brain activity. 1 H functional magnetic resonance spectroscopy (1 H-fMRS) at high magnetic fields allows for the non-invasive measurement of metabolic changes during brain activation. Optogenetics, on the other hand, has revolutionized the field of neuroscience. It was previously coupled with functional magnetic resonance imaging (fMRI) techniques in rodents enabling population-specific targeting of cells, investigating brain networks with unprecedented in vivo precision.
Introduction: Sleep-fragmentation (SF) is a common symptom associated to disturbances such as sle... more Introduction: Sleep-fragmentation (SF) is a common symptom associated to disturbances such as sleep apneas (1) Previous studies showed that SF induces daytime sleepiness and cognitive impairments associated to metabolic changes (2, 3). In the present study, the neurochemical profile of mice submitted to SF during 14 days was examined using H-MRS at 14.1T both in hippocampus and the frontal cortex. The goal of this study was to investigate changes linking sleep fragmentation to modifications in neurotransmitter concentrations. Materials and Methods: Animal preparation: C57BL6 mice (n=10, BW=25±2g) were individually transferred in rotating Plexiglas cylindrical cages equipped with three internal Plexiglas static walls to be submitted to SF. The rotations consisted in a mild rotation (1.5 rpm) of the floor of the cages lasting 20s every minute. Such a rotation brings the mouse in contact with one of the walls and wakes it up. Animals had free access to food and water. Each mouse was left to adapt to its new environment for a week before the first MRS session and prior to the start of the cage rotation to prevent stress. Mice underwent a first MRS session in their basal state and a second MRS 14days after .Prior to MRS, mice were gently manipulated to avoid stress and anesthetized with 2% isoflurane in a mixture of O2 and N2O. Each of them was positioned in a dedicated mouse holder equipped with ear and teeth bars and anesthetized with 1% isoflurane in O2/N2O through a nose cone. Body temperature was maintained at 36.5±1oC by circulating warm water around the animals.H-MRS All the experiments were performed on a 14.1T/26cm horizontal bore magnet ( Magnex, Varian). A quadrature T/R 14-mm surface coil was used. Localized proton spectroscopy was performed using SPECIAL (4) in a 4±1μl voxel for the hippocampus and in a 12±1μl voxel for the frontal cortex placed using multi-slice fast spin echo (FSEMS) images. Field homogeneities were adjusted using FASTMAP (5) up to water linewidth=20-25Hz. At least 40 blocks of 16 FIDs were acquired for a total acquisition time of 40minutes. Metabolite concentrations were calculated using LCmodel (6). A paired t-test was used to compare pre and post-SF metabolite concentrations. A pvalue<0.05 was considered significant. Results: Fig.1a and 1b present the comparison of mean metabolite concentrations pre and post-SF in the hippocampus and the frontal cortex respectively. In the hippocampus, mean GABA concentrations decreased significantly between basal and SF states (pvalue =0.006) and a significant decrease was also detected for lactate (pvalue<0.05). In the cortex, no significant differences were observed between basal and SF states, however a tendency to decrease was also observed for GABA (pvalue=0.21). In Fig.2, the evolution of GABA, and Lactate concentrations between basal and SF states are shown individually in the hippocampus (Black) and in the cortex (red).
Target Audience: Physicist, Neuroscientists, Biochemists Introduction: Recently, the importance o... more Target Audience: Physicist, Neuroscientists, Biochemists Introduction: Recently, the importance of thalamocortical projections (TC) to the primary somatosensory cortex (S1) has generated a lot of interest 1 .Thalamic nuclei such as the VPM and POM represent an important relay for functional information processing of the ascending response to whisker or forepaw stimulations. Moreover, TC inputs to S1 are known to modulate both glutamatergic and GABAergic transmissions 2. However, the metabolic mechanisms of regulation of the barrel cortex by TC transmissions remain unclear. Changes of metabolite concentrations in S1 of rats during stimulation have been evaluated using functional proton magnetic resonance spectroscopy (fMRS) 3,4. In the present study, fMRS was conducted in the primary somatosensory barrel field cortex and in the thalamus during rest and functional stimulation. In addition, the underlying mechanisms of glutamatergic and GABAergic transmissions from thalamus to barrel c...
An improved activity-induced manganese-dependent MRI study of the rat barrel cortex Purpose: In 1... more An improved activity-induced manganese-dependent MRI study of the rat barrel cortex Purpose: In 1997, Lin et al. (1) proposed an alternative to BOLD functional MRI to image brain function using Manganese. The paramagnetic properties of Mn2+ ions allowed for the first time the indirect measurement of neuronal activation through activity-induced manganese-dependent (AIM) MRI. However, the technique highly depends on the permeability of Mn2+ ions through the blood brain barrier and the minimization of their toxicity. Aoki et al. (2,3) further described the potential of AIM MRI and ways to overcome these difficulties. Nonetheless, although the technique is very attractive and promising for direct monitoring of regional brain activation independent of hemodynamic changes, it remains difficult and has not yet been extensively used. Here, we propose an optimized AIM MRI investigation of the rat somatosensory cortex under tight physiological follow up and an histogram analysis for an increa...
ABSTRACTThe electronic and nuclear stopping effects produced by MeV ion bombardment in polyethyle... more ABSTRACTThe electronic and nuclear stopping effects produced by MeV ion bombardment in polyethylene (PE) and polyvinylidene chloride (PVDC) have been previously studied and reported. We have subsequently selected two other insulators: polystyrene (PS) and polyethersulfone (PES) which contains sulfur as a crosslinking agent, and irradiated them with MeV alpha particles. The electronic and nuclear effects of the incident ions were separated by stacking thin films of the polymers. A layered system was selected such that the first layers experienced most of the effects of the electronic energy deposited and the last layers received most of the effects of the nuclear stopping. The changes in the chemical structure were measured by residual gas analysis (RGA), Raman microprobe analysis, RBS and FTIR. The post-irradiation characterization resolved the effects of the stopping powers on the PS and PES and the results were compared with those from PE and PVDC.
By definition, tumours are heterogeneous. They are defined by marked differences in cells, microe... more By definition, tumours are heterogeneous. They are defined by marked differences in cells, microenvironmental factors (oxygenation levels, pH, VEGF, VPF and TGF-α) metabolism, vasculature, structure and function that in turn translate into heterogeneous drug delivery and therapeutic outcome. Ways to estimate quantitatively tumour heterogeneity can improve drug discovery, treatment planning and therapeutic responses. It is therefore of paramount importance to have reliable and reproducible biomarkers of cancerous lesions' heterogeneity. During the past decade, the number of studies using histogram approaches increased drastically with various magnetic resonance imaging (MRI) techniques (DCE-MRI, DWI, SWI etc.) although information on tumour heterogeneity remains poorly exploited. This fact can be attributed to a poor knowledge of the available metrics and of their specific meaning as well as to the lack of literature references to standardised histogram methods with which surroga...
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